Emerald Ash Borer

adult ash borer

ash-habitatWhat It Is

Emerald Ash Borer (EAB) Agrilus planipennis is a destructive non-native beetle that feeds under the bark of ash trees and eventually kills them.  It affects species of Ash in the genus Fraxinus.

Where It Has Been Found

Originally from Asia, EAB was discovered in Michigan in 2002 and has been found in 29 states. It is estimated that it has killed over 60 million trees.

EAB was first found in Colorado in 2013 in the city of Boulder. Since then it has also been found in areas of Adams, Boulder, Broomfield and Larimer counties. It has not been found in Jefferson County.

USDA has established quarantine areas. Ash wood, trees or seedlings from the infested areas may not be brought into Jefferson County.  

Potential Impacts

Ash trees account for approximately 15% of the trees in our urban forests.  When we lose our trees to pests, we also lose the many environmental benefits trees bring to our neighborhoods.  

Environmental Benefits of Urban Trees

  • Capture rainfall and reduce runoff
  • Shade provides cooling and reduces energy use
  • Provide diversity for insects and wildlife

Building Resiliency in Urban Forests

Homeowners can contribute to the health of our urban forests by planting a variety of trees.  Having a mix of species reduces the impacts of pests like EAB that feed on a very limited host range.

List of Alternatives to Ash

EAB Identification

EAB is a green metallic beetle that is about 1/2-3/4 inch long and 1/8 inch wide. The adult beetles emerge from the trunk and branches of the ash tree in May- early June through "D" shaped holes.  Adults feed on the trees’ foliage and live 2-3 weeks.

The larva (immature stage) are white, segmented with a dark head.  They feed in S-shaped galleries under the bark.

View Lifecycle

Colorado State University Fact Sheet

How to Know if You Have an Ash Tree

Ash are medium to large trees with grayish bark that has distinctive diamond grooves when mature. Leaves, twigs, and branches are arranged in an opposite pattern.  Leaves are divided into leaflets arranged in 5-9 opposite pairs.

Michigan Extension Fact Sheet 2005

What You Can Do

If You Have an Ash Tree

If you have an ash tree you need to evaluate and plan for their protection or removal.  Your choice of actions and urgency will depend on factors that include the current health of the tree, the costs of treatment and removal, and how close you are to known infestations. 

  • Planting a diverse urban forest makes it more resistant to pests.
  • Once a tree becomes infested it will die unless you are able to treat it soon after it becomes infested.

Managing Emerald Ash Borer: Decision Guide


Within 2 miles of known infestation

If you have an ash tree on your property and you are within 2 miles of the known infestations you need to decide if you will remove or treat your ash trees.  

Treatment needs to occur in April-May.  If you hire a contractor, they need to be licensed as a Commercial Applicator by the Colorado Department of Agriculture.

More than 2 miles of known location

If you have an ash tree on your property and you are more than 2 miles of the known infestations you should:

  • Monitor your trees and look for thinning in the upper canopy
  • Water regularly including winter and fall watering
  • You may want to plan on their eventual replacement with a different type of tree
  • If there are no signs of decline it is not necessary to treat unless there are other insect pests affecting your ash trees

Front Range Tree Recommendation List©  

Insecticide Options for Protecting Ash Trees from EAB

Managing Emerald Ash Borer: Decision Guide

Don’t Move It

Because EAB can survive in ash wood, it is best if you do not move it unless you take precautions.

EAB Options for safe handling of Ash-Tree Wood

Firewood and Pests Recommendations 

Biological Control

Colorado is working with USDA APHIS to develop biological control agents that may control EAB.  

USDA’s Emerald Ash Borer Biocontrol Program

What Others are Doing

Jefferson County

CSU Extension


Wheat Ridge




Colorado Department of Agriculture

CSU Extension



Additional Information

Colorado Department of Agriculture - Emerald Ash Borer website

Ash Tree ID - Michigan


EAB Decision Guide

EAB Frequently Asked Questions - CSU

Emerald Ash Borer Information Network

ISA - Arborists

The North Central IPM Center Treatment Option Guide